1. Field of the Invention
The present invention relates to planetary-roller-type continuously variable transmissions disposed between a driving mechanism and a mechanism being driven, and also relates to planetary-roller-type continuously variable transmissions suitable for use in cases where the rotation speed ratio of the output shaft to the input shaft thereof is minutely adjusted or intentionally controlled, centered around a predetermined speed ratio, including 1:1.
This application is based on patent application No. 2004-173019 filed in Japan, the content of which is incorporated herein by reference.
2. Description of Related Art
Until now, there has been a great demand for continuously variable transmissions. For example, in the case where the driving mechanism is an electric motor, when changes occur in the operating environment, such as the voltage supplied to the electric motor, it may not be possible to obtain the predetermined rotation speed ratio between the output shaft of the electric motor and the input shaft of the mechanism being driven. In such an event, it is necessary to adjust the rotation speed ratio by means of a mechanical adjuster.
Also, when winding threads in spinning mills, the length of the circumference for winding up the thread changes as thread winding proceeds, and therefore, it is necessary to adjust the thread winding speed. As means to solve these problems, apparatuses such as chain-type continuously variable transmissions have been used.
In recent years, it has become necessary to carry out rotation speed ratio adjustment in the fields of printing presses, measurement instruments, vehicular steering systems, and so on, and there have been demands for high-quality power transmission devices producing low noise and having compactness, extremely low backlash, extremely low rotation variation, high efficiency, high reliability, and so on.
An example of this type of technology is given in Japanese Patent Application Publication No. 2004-58896, which discloses a steering apparatus including a differential transmission mechanism in a steer-by-wire system.